We propose to analyze the mechanism by which Friend leukemia virus suppresses T and B lymphocyte functions in mice. We further propose to examine the hemopoietic and immunologic requirements for viral transformation of stem cells into leukemic cells. We will analyze the viral interference between a non-oncogenic virus, lymphochoriomeningitis (LCM) virus, with Friend leukemia virus. LCM virus prevents leukemia when injected along with Friend virus, and we plan to assess the ability of this virus to "cure" leukemic mice exposed to total-body irradiation and transplanted with histocompatible marrow cells from donors genetically resistant to Friend leukemia virus.